Common-Mode Noise Reduction by Current Cancellation in Balanced Buck-Boost Switching Converter

Because conventional switching converters are usually using unbalanced circuit topologies, parasitic capacitance between the drain of an MOS-FET and the frame ground through its heat sink may generate the common-mode conducted noise. We proposed a concept of balanced switching converter circuit, which is an effective way to reduce the common-mode conducted noise of a switching converter by current cancellation. In this paper, the path of the noise current in a balanced buck-boost converter circuit is investigated using a current probe. By measuring current waveforms and frequency spectra of the parasitic capacitances and the frame ground line, the mechanism of the common-mode noise reduction by current cancellation is clarified.